PREHEAT oven to 350°F. Mix 2 pkt. of the cereal, the flour, baking powder, baking soda and salt; set aside. Beat 1/2 cup of the margarine and the brown sugar in large bowl with electric mixer on medium speed until well blended. Add egg; mix well. Add flour mixture alternately with the buttermilk, beating well after each addition. Spread into greased 13x9-inch baking pan.